Hello Iwilldecide,
It's sounds like you did the best you could by texting an apology. For me that's sounds like enough for now. A simple 'I'm sorry you feel like that... ,' if she brings it up again validates her and then nothing more needs saying from you after that.
Have you read around the lessons especially communication techniques for dealing with pwBPD?
Here is a link for you,
https://bpdfamily.com/message_board/index.php?topic=56206. Take your time and read around the subject, if you want to spend time as a group and are good friends with her boyfriend there are ways of helping avoid conflict for you all that might help you maintain all your friendships.
It might also help to involve your boyfriend in what you learn as this is also the girlfriend of his best friend. Do you think he is aware that there are some difficulties as well?